High-frequency amplifiers, radio transmitters, and the like



June 27, 1950 REEN El AL 2,512.742

E. G HIGH-FREQUENCY AMPLIFIERS, RADIO TRANSMITTERS, AND THE LIKE Filed Dec. 12, 1947 2 Sheets-Sheet 2 FROM! FROM/Q2 FROM R2 INZENTORS ERNEST. GREEN VICTOR OWEN STOKES BY f ATTORNEY Patented June 2 7, 1950 HIGH-FREQUENCY AlVIPLIFIERS, RADIO TRANSMITTERS, AND THE LIKE Ernest Green and Victor Owen Stokes, Chelmsford, England, assignors to Radio Corporation of America, a corporation of Delaware Application December 12, 1947, Serial No. 791,212 In Great Britain December 6, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires December 6, 1966 Claims.

This invention relates to high frequency amplifiers, radio transmitters and other apparatus of the kind in which, in order to obtain a large output power, two output stages driven by a common driving unit and supplying a common load circuit are employed.

Arrangements in which a common driving unit drives two output stages (hereinafter called final stages) which feed into a common load are frequently employed in radio transmitters. How ever, a difiiculty which is often experienced is that if the operating frequency is high and there is a number of intermediate stages-either fre quency multiplier or amplifiers or bothbetween the common driving unit and the final stages feeding the common load, relative phase shift between the outputs from the final stage may occur causing overloading and inefficiency. The main object of the present invention is to avoid this dimculty.

According to this invention a high frequency arran ement of the kind in which a common load is fed from a plurality of final stages driven by a common driving source comprises means, operated in dependence upon the relative phase or phases between the outputs of the final stages, for automatically controlling the tunin of at least one circuit in each of the channels to said final stage output circuits or in all but one of said channels so as to automatically vary said tuning in a direction to correct for any departure of said relative phase or phases from a predetermined value or values. In practice the predetermined relative phase or phases will, in general, be that of the in-phase condition.

The automatic tuning control may be applied in all the channels leading to the final stages or the objects of the invention can be achieved by eifecting automatic tuning control in all but one of the channels. In the simplest case Where there are only two channels the objects of the invention can be achieved, therefore, by applying automatic tuning control in only one channel but in this case control in both channels is preferred.

Preferably also the automatic tuning control is effected by one or more electron discharge tubes connected and operated to act as variable reactances which are controlled by the output or outputs from a phase discriminator circuit or 2 circuits actuated by energy taken from the final stages.

The invention is illustrated in the accompanying diagrammatic drawings, in which like references are used for like parts.

Figure 1 shows, in block form, the general arrangement of one embodiment of the invention.

Figure 2 shows a preferred'and very simple form of phase discriminator circuit in accordance with the present invention.

Figure 3 shows a form of phase discriminator which may be employed as an alternative to that of Fig. 2.

Figure 4 shows single double-controlled variable reactance tube which may be used instead of the two reactance tubes of Fig. 1.

Referring first to Fig. 1 which shows, in block diagram form, the general arrangement of one embodiment of the invention, the radio transmitter installation therein represented comprises a common drive unit I driving through two separate channels generally designated 2, 3 two final output stages 4, 5 which supply energy to a common load 6. Each channel includes a. desired number of frequency multipliers and/or amplifiers 1, 8 in cascade. Automatic tuning control is effected preferably at an early stage in each channel by means of tubes operated as variable reactance tubes, there being one such variable reactance tube appropriate to each channel. These tubes are included, in Fig. l. in the blocks 9, I0. Outputs from the two stages 4, 5, are fed as usual to the common load 6 and also to a phase discriminator network II which provides control potentials in dependence upon the relative phase between the final stage outputs, said control potentials being fed back to the reactance tubes at 9, l 0 to control the effective reactances presented thereby. The reactance tubes are, of course, included in the frequency determining circuit whose tuning i t b trolled and the automatic control is such that if the final stages depart from the desired inphase relation the tuning of the circuits with which the reactance tubes are associated are oppositely varied to correct for such departure.

The actual discriminator circuits and reactive tube circuits may take any of a variety of forms. A preferred and very simple form of phase discriminator circuit in accordance with the pres- 3 nt invention is shown in Fig. 2 which is a representation of the transmitter installation of Fig. 1 in more detail. In Fig. 2 the phase discriminator circuit, generally designated ll, comprises a pair of diodes V2V2' (or other rectifiers) whose anodes are connected together through a resistance R1 shunted by a first parallel tuned circuit C1L1. The cathodes of the diodes are connected to earth through separate load resistances R2R2 each shunted by a suitable bypass condenser as shown. If desired, meters M, M may be included in series with the load resistances. connected between the mid-point of the coil .or condenser of the tuned circuit LiC and earth. As shown the coil L1 is centre tappedfor thispurpose. These two tuned circuits are coupled as-indicated by the arrows one to each of the output circuits of the final stages 4, :5 said couplingbeing preferably effected as near to the common load circuit 6 as possible. The coupling .mayconveniently be effected inductively between thecoils L1Lz of the tuned circuits and the feeders from the stages 4, 5 to the common load circuit "6 and if desired, the said coupling may be adjustable. An adjustabletap on each diode load resistance R2R2' is connected through a suitable further resistanceRsRs' and/or bias supply '(not' shown) to thecontrol electrodeof one or other .of two variable reactance tubes Ii-V15, associated with tuned,

circuits L303, Ls'Gs' 'ingthe early sta es, 9, ll! in the channels 2, {from the common drive unit l. If the-phase discriminator is arranged to;give an output of negative polarity no :bias supply sources in the leads to the .gridsof- Vilh will ,be required. Ihe variable reactance tube circuits may be of any kind .known per se, for example, they may include pentodes and provision may be made for manual adjustment, e; g. byptoviding them with variable cathode leg resistances; R4124 as; indicated.

The first tunedcircuit L101 connected between theanodes ,of ethezdiodes is tuned substantially to resonance at the working frequency, whilethe second :tuned. circuit. LzCz is resonant at a. frequency .well jawayz-from this frequency. Thus the voltage acrossthese-two circuits when the two final stage output currents are in phase willbe nearly insquadratureandcan be adjusted acoue rately. inpquadrature by slightly mistuning the f rst; ;tuned circuit L101. Assuming symmetry in,

the diode circuits. the rectified currents inthe loadresistances RzRz will be equal so longrasthe.

quadrature relation is;maintaine d but if the cur.- rents fromthe final-stages 4, 5 depart from the in-phaserel ation the currentsin thesaid load resistances R2325 will become unequal and't'he consequent control voltages gfedbackto the reactance tubes V1V1i will producetuning changes, in the two channels to correct for the inequality, e. g. tov correct,forgdepartures from the desiredinphase relation.

An auxiliary monitor circuitinotshown) comprisingan addition'altuned circuit and a rectifier and meter equallybut oppositely coupled to bothfeedersshould'be providedinprder to insure. thatthe final stage outputs are in correct phase and not 180 apart. The'meter will give a minimum reading. when the phasing is correct. Such--,a .monit0r circuit-may be, arranged to operate visual and/or aural indicating meanswhen a predetermined level is exceeded and automatically, to open th main H. T. supplies when astillhigher predetermined level ishpassed so :as

to provide automatic protection against damage,

A second parallel tuned. circuit CzLz is;

'trol grids through .a suitable resistance R5.

in the event of a failure of the automatic phase sensitive control means.

Obviously only one diode or other rectifier may be employed and phase control applied to one channel only, the other being set to a mean phase. The symmetrical arrangement of Figs. 1 and 2 is, however, preferred.

In a modified form of phase discriminator shown in Fig. 3 and which may be employed as an alternative to that of Fig. 2 the diodes V2, V2 are replaced by grid controlled tubes GVzGVz' for example triodes as shown, having their conconnected together and earthed The first or in-tune parallel tuned circuit L1C1 shunted by resistance R1 is. connected between the anodes of the triod'es and the mid-point of the coil of this circuit is earthed. The second or off-tune parallel tuned circuit L202 is connected between the common grid point of the triodes and earth. In other respects the phase discriminator is as in Fig. 2 and control voltages for the reactance tubes V1V1" (not shown in Fig. 3) are taken off from taps on resistances RzRz' in the cathode legs of the triodes GVzGVa'. Again as before, the circuit settings are suchas to obtain a quadrature relation between the voltages'a'citoss the two parallel tuned circuits L1C1, LzCzwhen-the (outputs from the final stagesare in-phase.

It isnot necessary to provide-two-separate variable reactance tubes such as V1-V1f, -one in association with each channel 2, 3.:fOIf --2.- shown in Fig. 4 a single double-controlled variable reactance tube V11 ma be employed in conjunction with a symmetrical phasediscriminator network such as that-shown in Fig..2.or in Big. 3 by applying one controlling .cutput irom Rz of the discriminator, network (notshowninifig. 4) .to. a grid-of the reactance tube V11 and the other con-. trolling output from-R2 to'another electrode, for. example, the cathode of the said tube .V11.

ln some cases the .output stages ll, 5 may be usedas a phase discriminator, because when the relative; phase of theoutputs a from twochannels changes in one sense the anode feed ofoneoutput.

stage will rise whilstthat of the other" will fa 11- When the relative phasepchanges in the opposite sense these. conditions, arereversed. Resistances connected between the, cathodes and earth in the output stages .4, scan be used-to. provide two voltages to control the reactance valve or; valves in the same-way asv before.

Wherethe outputspf'severalfinal stages are:to.

be supplied to a common load, .itcis, preferred to use one output; stage as areference, providingphase discriminators, and .monitors tocompare the phase-of1 all other outputs with this. :Each phase discriminator. would then control. a reactancevalve in its .-own transmitter.

Where a common modulation is appliedto the;

final stagenoutputs means shouldrbe'provided .for preventing such modulation from.=affecting the operation of the reactance. tube .or :tubes. Such means may take anyconvenient form known .per se, forexamplesmoothing and :Iimiting circuits.

What is claimed is: 1. In a circuit arrangement for maintaining an in-phaserelation between alternating volages fed by a pluralityof signal channels to-acommon load, means responsive to the -relative.

phase between thev outputs :of said channeled-or developing a .control :voltage of a-magnitude dependent upon. such relative phase, voltage responsive means inat leastone of saidachanne'ls for controlling :th tuning .ofsuch channel, and

means for applying said control voltage to said last-named means to vary the tuning of the'controlled channel in a direction to correct for any departure of said relative phase from-a predetermined value. y

2. In a circuitarrangement for maintaining an in-phase relation between alternating voltages fed by a pair of signal channels; from a common driving source to a common load, means responsive to the relative phase between the outputs of said channels for developing a pair of control voltages of magnitudes dependent upon such relative phase, separate voltage responsive means in each of said channels for controlling the tuning of such channels, and means for applying said control voltages separately to each of said last-named means to vary the tuning of each corresponding channel in a direction to correct for any departure of said relative phase from a predetermined value.

3. In a circuit arrangement for maintaining an in-phase relation between alternating voltages fed by a plurality of signal channels to a common load, means responsive to the relative phase between the outputs of said channels for developing a control voltage of a magnitude dependent upon such relative phase, variable reactance tube means in at least one of said channels for controlling the tuning of such channel in response to a voltage applied to such means, and means for applying said control voltage to said reactance tube means to vary the tuning of the controlled channel in a direction to correct for any departure of said relative phase from a predetermined value.

4. A circuit arrangement as defined in claim 3, wherein a separate variable reactance tube is provided for controlling tuning of each channel which is subjected to such control, wherein the control voltage developing means produces a plurality of control voltages, and wherein each such tube has applied thereto a separate single control voltage from the control voltage developing means.

5. A circuit arrangement as defined in claim 3, wherein a single grid-controlled variable reactance tube is provided for controlling tuning of one channel which is subjected to such control, wherein the control voltage developing means produces two control voltages, and wherein said single tube has applied thereto said two voltages from the control voltage developing means, one voltage being applied to the cathode of said tube and the other to the grid of said tube.

6. In a circuit arrangement for maintaining an in-phase relation between alternating voltages fed by a plurality of signal channels to a common load, at least one discriminator circuit having a pair of input resonant circuits, one of which is resonant at substantially the predetermined output frequency of the channels and the other of which is resonant at a frequency displaced therefrom, said resonant circuits being coupled each to a separate one of the channel outputs adjacent the common load, means connecting said resonant circuits in a rectifier circuit providing two equal control output potentials so long and only so long as the voltages across the two resonant circuits are substantially in phase quadrature, separate voltage responsive means in two of said channels for controlling the tuning of such channels, and means for applying said two control output potentials separately to each of said last-named means to vary the tuning of each corresponding channel in a, direction to correct for any departure of the voltages across the two resonant circuits from a phase quadrature relationship.

7. A circuit arrangement as defined in claim 6, wherein the rectifier circuit includes two rectifiers, wherein said one resonant circuit is centertapped and connected between corresponding terminals of said rectifiers, and wherein said other resonant circuit is connected between said center tapand a point of fixed potential, said rectifiers having impedances, connected. respectively between the remaining terminals thereof and a point of fixed potential, in which said two control output potentials respectively appear.

8. A circuit arrangement as defined in claim 6, wherein the rectifier circuit includes two gridcontrolled tubes having a common grid terminal connected to a point of fixed potential through an impedance, wherein said one resonant circuit is connected between the anodes of said tubes and has its center point connected to a point of fixed potential, and wherein said other resonant circuit is connected between said common grid terminal and a point of fixed potential, said tubes having impedances, connected respectively between the cathodes thereof and a point of fixed potential, in which said two control output potentials respectively appear.

9. In a circuit arrangement for maintaining an in-phase relation between alternating voltages fed by a pair of signal channels to a, common load, said channels each including an input stage having therein a circuit the tuning of which determines, at least in part, the relative phases of the alternating voltages fed to said load: a reactance tube in each of said channels connected in shunt to the said circuit therein for tuning the same; a discriminating and detecting network coupled to the outputs of both of said channels for comparing the phases of the voltages fed by the channels to the said common load, said network including a plurality of electron discharge devices connected in rectifier circuits having impedances wherein potentials are developed of a magnitude dependent on the relative phase of the alternating voltages in the outputs of the channels; and means for applying said developed potentials separately to the control electrodes of corresponding reactance tubes.

10. In a circuit arrangement for maintaining an in-phase relation between alternating voltages fed by two signal channels to a common load, said channels each including an input stage having therein a circuit the tuning of which determines at least in part the relative phases of the alternating voltages fed to said load: a reactance tube in each of said channels connected in shunt to the said circuit therein for tuning the same; a discriminating and detecting network coupled to the outputs of both of said channels for comparing the phases of the voltages fed by the channels to the said common load, said network including a pair of electron discharge devices each having a cathode connected to ground by an impedance, a resonant circuit coupled to the output of one channel and connected between like electrodes of said tubes, and a circuit detuned with respect to said last-named circuit coupled to the output of the other channel and connected cophasally to like electrodes of said tubes, whereby potentials of a magnitude dependent on the relative phase of the alternating voltages in the outputs of the channels are developed in said impedances; means for applying one of the developed potentials to the control electrode 01 7 8 one ofithereacfnancetubes; andnneansiorapply- Number; Name Date ing-:.the other: devel'opedivpoteniciali tenths; cont-r01 2;084=,-836-, Buschbeok June 22, 1937 electrode ofrtheocher reactanaemube; 2,196,592 Koch "Apr. 9, 1940 ERNEST GREEDL. 2337, 514. White; v Apr. 8-, 1941 VICTOR OWEN, STGKES. :5 2,273,161 Usselman Feb. 17, 1942 e 2,286,396 Trevor "June 16, 1942 REFERENCES CITED 2, 304' 377 Roberts Dec. 8, 1942 The f01 10wing references arev of recordimthe 53 Peterson Oct 19, 1943 1518 of thls Patent 2,411,376 Hansen Dec. 3, 1946 UNITEDHSTATES PATENTS; 10 2.;425 981: Bardzet-val Aug. 19, 1947 Number Name Date 754,382- Clement Apr. 15,1 1930 

